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Hot Tub Care

Chemistry Ranges

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Hot Tubs and Spas are very popular, and they can be a great leisure item to invest in. They are relatively inexpensive and can fit easily in even the smallest backyard space. Once you purchase one you will need to hire a service company to maintain the chemistry for you or you can do it yourself. The chemistry is similar to a backyard pool with some slight differences.


The first and main difference is the small body of water that you are dealing with. A typical backyard pool has 15,000 gallons and a Hot Tub usually has 250-400 gallons of water in it. The chemistry adjustments, therefore, need to be done in small doses, measured in teaspoons vs gallons or pounds. So a little really goes a long way in a Hot Tub. For example, if a 300 gallon Hot Tub has a zero chlorine reading you would just need 6 teaspoons of 12.5% liquid chlorine to raise it to 3 ppm.


Since they are often heated to 100 degrees all of the time be aware that the chemicals in the spa will burn off much faster than they would in a conventional inground pool. Since they are covered and out of the sun there is also no need for Conditioner (cyanuric acid) to protect the chlorine from the Sun’s UV Rays. Also, if you are using bromine Conditioner is not compatible with it anyway so there is no need to add it to your Hot Tub.


You need to have some idea of how much water is in your Hot Tub. The easy way to do this is to find your manufacturer brand and model number and then go to their website or call them and ask how many gallons are in that particular model. Typically a Hot Tub will be 250 to 400 gallons so yours will be in that range.


You also need a way to calculate the dosage to add to balance your Hot Tub water. The easiest way to do this is to use a Chem Dosage App like

These apps will give you the exact amount of chemicals to add to achieve your desired levels based on your Hot Tub size in gallons.


Here are the Ideal Levels for your Hot Tub:

Free Chlorine or Bromine ppm: Min 1.0 (Ideal 2.0-4.0) Max 5.0

pH: Min 7.2 (Ideal 7.4-7.6) Max 7.8

Total Alkalinity ppm:  Min 80 (Ideal 80-120) Max 120

Calcium Hardness ppm: min 150 (Ideal 150-250) Max 250


Chlorine and Bromine are the primary sanitizers that you will use in your Hot Tub. You would use either of these two exclusively and not combine them in your Hot Tub. If you are using Bromine Tablets you would therefore not use liquid chlorine. I prefer using chlorine since it is easy to add and measure and it is highly effective. Bromine is also a good choice and having tablets available is convenient in helping you maintain your Hot Tub sanitizer level all week long. You just want to make sure you don’t overdo it since it is a very small body of water and a little really goes a long way.


UV System:

UV is a very popular add on in a spa. It enhances the sanitation of the water and will allow you to use less chlorine and bromine. UV light systems work by irradiating the water, as it passes by a UV lamp the specific wavelength UV spectrum (254 nm) hits the water. When exposed to UV light of this specific wavelength, living particles have their DNA rearranged and become unable to reproduce, thus destroying algae, bacteria, and viruses. They are highly effective and are included with many new spas sold on the market today.



Ozone Systems are another way to enhance your Hot Tub sanitation. An Ozonator system duplicates the natural oxidation process that exists in nature and produces ozone safely and in controlled amounts. When used with bromine or chlorine, ozone can reduce the amount needed to sanitize the water and you can run your Hot Tub with as little as 1 ppm of each. An Ozone System destroys microorganisms and breaks down harmful chemicals that cause total dissolved solids to gather, thus increasing filtration of the water. The water will stay cleaner and clearer with an Ozone System running in your Hot Tub.


Low pH or low Alkalinity - Sodium Bicarbonate:

If the pH or Alkalinity falls below the ideal levels you can easily raise both with sodium bicarbonate. The most familiar product on the market and one you can readily use is Baking Soda. Sodium bicarbonate is also sold under the label as Spa pH Up, Spa Alkalinity Up, pH Increaser and any common name that indicates the product raises the pH and Alkalinity. So look for a product with the active ingredient of sodium bicarbonate or just purchase a bag of Baking Soda and use that to raise the pH and Alkalinity in your Hot Tub.


High pH or high Alkalinity - Sodium Bisulfate:

If the pH or Alkalinity gets above the ideal levels, you can easily lower it with dry acid or sodium bisulfate. It is sold under the label of, Spa pH down, pH down, pH Decreaser, Dry Acid or anything with the active ingredient of sodium bisulfate. Remember a little goes a long way so do not overdo it or you will soon be adding sodium bicarbonate to bring the level back up.


High or Low Calcium Hardness  - Drain the Spa or add Calcium Chloride:

The calcium level in your Hot Tub will pretty much match your fill water. So, if you have hard water in your area your spa will likely have high calcium also. The only way to lower it is to drain the spa. So you may need to drain your spa more often to keep the calcium hardness in range. If your calcium hardness is low you can add a small amount of calcium chloride to raise it up.


If the water starts to exhibit any of the following it is time to drain it and refill it with fresh water. A green or blue tint to the water indicates metal ions in the water. Drain and refill and add a metal sequestering agent like Leisure Time Metal Gon. If the water gets foamy this indicates that there are contaminants in the water or the Total Dissolve Solid (TDS) levels are high. Drain and refill if excessive foam persists. The water is cloudy and doesn’t clear up after adding a sanitizer and running the spa. Drain spa and clean or replace the filters. At any point of the water quality is compromised simply drain and refill.

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